Government Works Exception for Copyrights
Generally, copyright protection is not available for "any work of the United States Government." 17 U.S.C. Section 105. Any work that is "prepared by an officer or employee of the United States Government as a part of that person's official duties" constitutes a "work of the United States Government." 17 U.S.C. Section 101. Those works fall into the public domain.
Sometimes, however, copyrighted works are created by non-government personnel for the government, such as when the government commissions a piece of art. The artist later transfers the copyright to the government. The "government works exception" then allows the federal government to hold the copyrights for those works transferred to it by assignment.
Some have argued that the government is using this exception unfairly and as a workaround the copyright law. So far, it has been used to prevent the copying or creation of derivative works from items such as a film series on early Supreme Court cases to the Sacagawea coin.
The Vietnam Women's Memorial Foundation, Inc., ("VWMF") now is trying to use the exception as a basis to sue those who have sold photographs of the Vietnam Women's Memorial. The Memorial is a bronze sculpture created by Glenna Goodacre of Sante Fe. It resides on the grounds of the Vietnam Veterans Memorial in Washington, D.C., and depicts three women and a wounded soldier. Goodacre reportedly transferred the copyright to the sculpture to the VWMF, who is now suing various entities that allegedly sold photographs of the sculpture.
The VWMF claims copyright in the statue on its website. It would have been helpful to let photographers know the alleged copyright status of the statue (using a commonly known tool called the copyright notice) where it resides, which happens to be in a national park next to government works that are in the public domain.
How the VWMF case will shake out is hard to tell. But it's always best to determine the copyright status of a creative work before photographing it.
Take my advice; get professional help.